1. Install and enable pathauto module
2. Go to admin/config/search/path/patterns
3. E.g. I want all my content type Articles to have path of www.example.com/articles/my-article-title, so under Articles paths I put 'articles/[node:title]'
4. After you updated all your patterns, click Save and go under tab Bulk generate
5. Tick Content paths and hit Update.

Now your paths should be updated.

Also if it's some old paths and they are already indexed by Google and available in search results, you should add redirects for old paths to new paths with redirect module. Or you can wait till Google reindex your site if it's not important.